The routes through which electricity travels and makes things happen are called electric circuits. The picture on the left displays a very simple electric circuit. It contains a source of tension, a conductor and a resistor. When the poles of these components are connected, electricity begins to travel through the circuit. 

When electricity can travel through the circuit, we are talking about a closed circuit. This is very different from what the word "closed" means in everyday speech. 

When the circuit is cut at a certain point and electricity cannot travel through it, we are talking about an open circuit.